Gold surfaces exhibit most interesting frictional properties on the nanometer scale. They can be studied in detail by means of friction force microscopy. Atomic-scale variations of the lateral force allow investigation of microscopic mechanisms of sliding. Friction force microscopy even reveals surface reconstruction of the gold surface as a modulation of the lateral force signal. Experiments indicate that the mobility of surface atoms at room temperature and plastic deformation mechanisms give rise to neck formation between gold and microscopic asperities in sliding contact. The frictional properties of gold surfaces change dramatically at temperatures below 150 K, where the surface diffusion is greatly reduced. Insight into the lubrication properties of self-assembled monolayers is provided by molecular-scale modulations of frictional forces. Molecular-scale maps of the friction force also allow identification of the relevant surface structure in experiments on electrochemically modified gold surfaces. Variation of the electrochemical potential is a means to reversibly switch between low and high friction states on gold surfaces.

Grain size influences the mechanical strength of materials. In polycrystalline materials, strength increases with decreasing average grain size (for grains larger than 100 nm). This well-known Hall–Petch relationship typifies a strengthening mechanism, in which dislocation motion is impeded by grain boundaries. As grains become smaller, higher stresses are required to deform them. However, this formalism only considers the role of the “average” size of grains. Heterogeneous materials, however, have a broad “distribution” of grain sizes. Here we show that materials with narrowed grain size distributions have mechanical properties that differ from Hall–Petch predictions. Narrower distributions show increased strength, as their homogeneously sized grains yield at higher loads than the large grains in materials with broader grain size distributions. Plastic deformation depends on the coarsest grains, which yield first. These results suggest new routes for tailoring material properties.

From bone to dentin to nacre, biomaterials are structurally advanced composites with superior toughness and significant stiffness, based on simple building blocks. Here, using a series of molecular mechanics models with bioinspired topologies, we propose design mechanisms rooted in the simplest mechanical interactions—perfectly brittle linear elastic—which are shown to be sufficient to achieve superior toughness at high stiffness in biological composites. In a two-phase composite system, we show that by adapting the elastic constitutive laws of the matrix phase and by tuning the interactions of the constituents we can realize materials with a large range of combinations of toughness and stiffness. Notably, this can be achieved without changing the fracture energy of the individual composite components. Through a systematic analysis and the development of a simple model, we unveil basic design principles that lead to fundamental insights into the mechanics of natural composites for applications in a range of engineering disciplines.

Ordered arrays of titania nanotubes (NTs) are considered as good candidates for photocatalytic applications including water splitting. Considering that the functionality of these nanostructures is influenced by their morphology, electronic and the crystallographic structure, fundamental understanding of these properties and their possible correlations can clarify the approaches toward enhanced photocatalytic efficiency. In this work, ordered arrays of titania NTs are synthesized electrochemically and are subjected to isochronal annealing treatments in various atmospheres (oxygen-rich, oxygen-deficient and reducing) to modify their morphology, crystal and electronic structure. Upon characterization of these NTs, direct correlations are found between the annealing atmosphere and the corresponding unit cell volume and the crystallite size. Furthermore, correlations between the NTs’ structure and magnetic response are observed, revealing changes in the electronic structure such as the density of states, that are in turn relevant to the functional catalytic properties of titania.

A nanostructured surface layer was fabricated in the surface of 316L stainless steel by a novel fast multiple rotation rolling (FMRR) technique. The microstructure and the tensile properties of the treated sample were investigated in detail. The experimental results indicate that a nanograined (NG) film was successfully obtained in the surface of the sample. Equiaxed nanograins with the average grain size of about 12 nm are achieved in the surface layer. At the sample time, deformation-induced α-martensite is produced during the FMRR treatment. The volume fraction of martensite is about 20%. The yield strength (0.2% offset) of the sample, of which one side is of NG structure and the other is coarse grained (CG), is increased by 51% in comparison with that of the CG sample. Though the plasticity is diminished slightly for the FMRR specimen, the elongation still reaches a high value of about 38% owing to the contribution of the CG structure.

Carbon nanocoils (CNCs) with different diameters have been synthesized on different substrates by thermal chemical vapor deposition using Fe films as catalysts prepared by ion sputtering. It is found that CNCs with diameters greater than 100 nm are obtained as the main products in large quantities on Fe film coated indium tin oxide substrates. However, on Fe film coated SiO2 substrates, multiwall CNCs (MWCNCs) along with carbon nanotubes (CNTs) are grown, and the yield of MWCNCs is decreased rapidly with a lower Fe film thickness. The as-grown MWCNCs with observed coil diameters less than 100 nm and filament diameters less than 30 nm are much thinner than the conventional CNCs. Plate-like catalyst particles with sizes much larger than the filament diameter of the MWCNCs are observed at the roots of these MWCNCs, indicating a base growth mechanism. Furthermore, it is also observed that large particles with irregular shapes lead to the growth of helical MWCNCs, while large particles with steady circular shapes tend to grow as straight CNTs. Based on the experimental results, a growth model for MWCNCs is proposed.

Carbon nanotubes (CNTs) supported Pd nanoparticle (NP) catalysts (Pd/CNTs) were prepared by a green and facile synthesis method based on hydrogen-bonding self-assembly. The size and loading of Pd NPs on catalysts were easily controlled by tuning both the relative amount of citrate to Pd salt in the solution and the relative amount of Pd NPs to CNTs. The size of Pd NPs on as-prepared catalysts can be tuned in the range of 3–6 nm, and Pd loading can be controlled in the range of 0–19 wt%. The catalysts were characterized by Brunauer–Emmett–Teller measurement, x-ray diffraction spectroscopy, and x-ray photoelectron spectroscopy. The performance of Pd/CNTs catalysts was evaluated in the hydrogenation of nitrobenzene. Compared with the catalysts prepared by the impregnation method or supported on conventional supports, Pd/CNTs catalysts show relatively higher activity and selectivity. The recyclability tests indicate that the Pd/CNTs catalysts can be used at least five times without significant loss in activity and selectivity.

Under the strategies of doping to extend the absorptive response region of a semiconductor and fabricating a mesoporous structure with large specific surface area to enhance the photocatalytic property, an efficient visible-light-driven photocatalyst of bismuth-doped titanium dioxide (Bi/TiO2) was prepared via a facile sol-gel route. The resulting materials were characterized by powder x-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TG), UV–vis diffuse reflectance spectrum (DRS), and N2 adsorption–desorption measurements (BET). The photocatalytic performances of as-synthesized particles were monitored by degradation of 2,4-dichlorophenol (2,4-DCP) in transparent aqueous solutions under visible light illumination. The results revealed that mesoporous PEG-modified Bi-doped TiO2 exhibited much higher photocatalytic activities than Bi-doped TiO2 without modification, and noticeably the optimized doping level was increased from 2 to 4 mol%. The visible-light photocatalytic activity enhancement of PEG-modified Bi-doped TiO2 could be attributed to appropriate proportional mixed crystal phase, large surface area, porosity, mesoporous network with interconnected small nanocrystals, and its strong absorption in the visible region.

In this work, we succeeded in synthesis of spinel LiMn2O4 via a facile self-template method. The product displays a micro-/nanohybrid structure. Nanoparticles/plates act as the primary nanoblocks to build the secondary microarchitecture. There is the open space between the nanoblocks and the void space between the secondary structures. Electrochemical tests demonstrate that the as-synthesized sample exhibits superior rate capability and high-rate cycleability when contrasted with its solid counterpart. The initial discharge capacity is 126 mAh/g at 0.1 C, 110 mAh/g at 10 C, and 84 mAh/g at 20 C. The discharge capacity retention of about 80% is obtained after 800 cycles at 10 C. The high capacity and excellent cycling life of the material shows its potential for application as high-power batteries. The improved rate capability and cycleability can be attributed to its secondary structure that can facilitate fast Li-insertion/extraction and buffer the volume expansion/contraction upon cycling.

We study the behavior of fluorohectorite synthetic clay particles dispersed in paraffin wax. We report wide-angle x-ray scattering related to electric-field-induced alignment of the embedded clay particles. The development of anisotropic arrangement of the particles is measured during melting and crystallization of the composites. The degree of anisotropy is quantified by fitting azimuthal changes of the clay diffraction peak intensity to the Maier-Saupe function. This parametric function is then used to extract both the full width at half maximum (FWHM) and the amplitude of the anisotropic scattering and eventually to estimate a nematic order parameter for this system. Finally, the time evolution of the one-to-zero and zero-to-one water layer transition in paraffin embedded fluorohectorite clay galleries is presented, and we demonstrate that such particles can be used as “meso-detectors” for monitoring the local water content in bulk carrier matrices, such as paraffin wax.

Confined synthesis of three-dimensionally ordered mesoporous-imprinted (3DOm-i) zeolites within three-dimensionally ordered mesoporous (3DOm) carbons prepared from silica colloidal crystals was achieved through multiple hydrothermal (MHT) synthesis and steam-assisted crystallization (SAC). The transition of ordered mesoporous structures, starting from silica colloidal crystal to resulting 3DOm-i zeolites including the intermediate 3DOm carbon templates, and the correlations among the confined synthesis methods, crystal growth nature of different zeolites, and the sintering of the templates were studied. An imperfect replication was found in 3DOm-i zeolite when it compared to silica colloidal crystals regardless the synthesis methods (MHT or SAC), which might be originated from combination effects of sintering of the silica colloidal crystals and partial filling of cavities of the 3DOm carbon template during the confined synthesis, and the degree of the structure replication was notably influenced by microstructures of zeolite as well. A thorough investigation of the growth development of 3DOm-i BEA zeolites with various Si/Al ratios ranging from 14 to 27 through the MHT method confirmed that the crystallization takes place in the carbon template by a cage-to-cage propagation growth process.

Eu3+, Bi3+ codoped Lu2O3 powders (Eu = 2.5 at.%, Bi = 0–3.0 at.%) were prepared using the sol–gel method. Fourier transform infrared spectroscopy, x-ray diffraction, and excitation and emission spectra were carried out to characterize the synthesis, structure, and luminescent properties. The excitation spectra show a strong peak at 350–390 nm, corresponding to the Bi3+1S0 → 3P1 transition, and the emission spectra present the emission from 5D0 → 7FJ (J = 0, 1, 2, 3, 4) level of Eu3+. The intensity of the reddish emission at 612 nm was monitored as a function of the Bi3+ content and showed a light yield increment of ≈400% compared to a monodoped sample at 1.0% at. Bi3+, produced by an energy transfer process from Bi3+ to Eu3+. This was a consequence of the overlapping of the Bi3+3P1 → 1S0 emission with the f–f Eu3+ transitions.

During directional solidification of Cu–Ge peritectic alloys, a two-phase separated structure has been observed. With proper growth conditions, the peritectic ζ-Cu5Ge and primary α-Cu phases completely separate and form cylindrical layered structures. It is found that the formation of the separated structure is closely related to double diffusive convection and growth conditions. In the two-phase separated structure, a large trijunction region of peritectic reaction forms around the cylindrical α-Cu phase. During peritectic reaction, the morphological instabilities of ζ-Cu5Ge occur under high pulling velocities and are explained by the constitutional undercooling criterion. A new coupling growth between the ζ-Cu5Ge-phase and the groove of α-Cu phase near the trijunction is observed. Different from peritectic coupling growth, the diffusion coupling is established below the peritectic temperature. This two-phase separated growth process creates new opportunities for the fabrication of functionally layered materials.

The relationship between electric current direction and recrystallization rate as well as the resulting texture induced by electric current pulses (ECPs) was investigated in a Cu–Zn alloy. To distinguish the effect of electric current direction on recrystallization rate, the same input energy was exerted upon the samples to eliminate the effect of Joule heating induced by ECPs. Results showed that the recrystallization-related nucleation rate could be greatly enhanced when the electric current was dispositioned at an angle to the rolling direction. The main mechanism for the different nucleation rates might be ascribed to the different driving forces for recrystallization induced by ECPs when there was an angle between the electric current direction and the rolling direction.By all reckoning, it was expected that the ECP treatment would provide a promising approach for controlling the nucleation rate by changing the exerted electric current direction.

Microstructures and mechanical properties of the Mg–4Y–2.5Nd–0.6Zr (wt%) alloy in the as-cast, as-rolled, and rolled-T5 conditions have been investigated. Results showed that the as-cast sample mainly consisted of the α-Mg matrix, network-like Mg41Nd5 phase, and cuboid-shaped Mg24Y5 particles. For the as-rolled sample, the thermally stable Mg24Y5 particles located at both grain boundaries and matrix, and the average grain size was greatly refined to about 15 μm. Yield strength, ultimate tensile strength, and elongation of as-rolled samples were 290 MPa, 235 MPa, and 10%, respectively. They were enhanced by 48.7%, 56.7%, and 38.9% correspondingly compared with those of the as-cast sample. After isothermal aging at 250 °C for 4 h, the optimal mechanical properties can be obtained. Besides, the tensile strengths of as-rolled and rolled-T5 samples decreased gradually with a gradual increase of ductility from room temperature to 300 °C. Quasicleavage and cleavage fracture were the fracture patterns of as-rolled and rolled-T5 samples, respectively, at room temperature. For samples under the two conditions, fracture mode similarly changed with the increase of test temperatures, and ductile fracture can be observed at higher temperature.

The monomer dimethylaminoethyl methacrylate (DMAEMA) was cross-linked by clay Laponite XLG and Laponite XLS, respectively, in situ free-radical polymerization to prepare nanocomposite gels (named as G-NC gels and S-NC gels). From the analysis of yield, transparency, Fourier transform infrared spectroscopy, x-ray, and scanning electron microscopy, it was proved that the clay Laponite XLS is an appropriate cross-linker for preparing PDMAEMA NC gels with better homogeneous and higher yield due to the uniform dispersion of clay in gels. The resulting S-NC gels show obvious temperature and pH double sensitiveness, and the lowest critical solution temperatures of gels with a low clay content are close to the temperature of the human body, which makes this gel a potential candidate for application in drug release. Comparing with the gels cross-linked by a chemical cross-link agent, the S-NC gels exhibit a considerable improvement in the mechanical properties, swelling ratio, and deswelling rate. The properties of S-NC gels could be adjusted by controlling the content of clay.